1. Field of the Invention
The present invention relates to a projection type image display mechanism and a projection type image display device for enlarging an image and projecting the image on a screen by utilizing a light valve element such as an LCD panel.
2. Description of Related Art
A projection type image display device such as an LCD projector, a liquid crystal television, and a projection type display device, has been known as a device for enlarging an image on a light valve element and for projecting it on a screen by projecting light irradiated by a light source (lamp and the like) on the light valve element (for example, LCD panel and the like).
As for the projection type image display device, there have been raised problems that an LCD panel and the parts thereof are heated by absorbing light irradiated by the light source and that dust floats in the vicinity of the LCD panel. The extreme heating of the LCD panel and the parts thereof causes a malfunction (in the worst case, broken LCD panel) of the LCD panel, and floating dust in the vicinity of the light incidence/reflection plane of the LCD panel or in particular, the dust stuck to the LCD panel causes deterioration in quality of the image enlarged and projected on the screen (hereinafter referred to as the screen image).
Therefore, in many projection type image display devices, measures have been taken to solve these two problems.
For example, a certain projection type image display device has a cooling unit designed specifically for the LCD panel to prevent the LCD panel from being heated over a predetermined temperature (for example, about 60.degree. C.). This can ensure normal operation of the LCD panel constituted by optical functional members such as a semiconductor drive element, liquid crystal and the like. Further, for example, a light source which produces heat of about 30 percent of the input energy and radiates a large amount of input energy as thermal energy so as to remove light other than visible light (for example, light having a wavelength of 400 nm to 700 nm), that is, ultraviolet light (for example, light having a wavelength of less than 400 nm), or ultrared ray (for example, light having a wavelength of more than 700 nm), usually has a cooling unit designed specifically for the light source. The light source produces heat of more than half of the total input energy. In this respect, an air-cooled unit such as an air blowing fan is generally used as the cooling unit because it can be easily operated.
Further, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 7-152009, a transmittance type LCD panel is housed in a hermetically closed space so as to prevent dust from entering the vicinity of the LCD panel. Further, to prevent the LCD panel from being heated, air is circulated in the hermetically closed space.
In the image display device disclosed in the Japanese Unexamined Patent Publication No. 64-5174, to improve utilization efficiency of light in a high definition image, a reflection type LCD panel is employed and a reverse plane of the incidence/reflection plane thereof (hereinafter referred to as reverse plane") can be utilized as a radiation plane.
In the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230, to more effectively utilize a reverse plane of the reflection type LCD panel as a radiation plane, a cooling unit is provided on the back side of the reflection type LCD panel.
However, since the conventional projection type image display device is provided with an air blowing fan designed specifically for each heating body (a light source and a LCD panel), sufficient improvement has not been produced in reliability and costs of the device. Therefore, a simplified structure of a cooling mechanism is required. Further, the conventional projection type image display device has the problem that if an exhaust port faces a wrong direction, warm air exhausted from the exhaust port is blown over the audience and the screen image become unstable by the unstable air produced in the optical path of the light projected on the screen.
None of image display devices can solve both problems that the LCD panel and parts thereof are heated and that the dust floats in the vicinity of the light incidence/reflection plane of the LCD panel. That is, ensuring the reliability of the device and improving the quality of the image do not exist simultaneously in the prior art.
For example, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230 and in the image display device disclosed in the Japanese Unexamined Patent Publication No. 64-5174, as described above, measures have been taken to prevent the LCD panel from being heated but special measures have not been taken to prevent the dust from floating in the vicinity of the light incidence/reflection plane of the LCD panel. Therefore, there is an extremely high possibility that the shadow of the dust is seen in the screen image. Further, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230, the whole device is heated but only the LCD panel is locally cooled, which does not produce a sufficient cooling effect. Therefore, the reliability of the whole device can not be ensured.
On the other hand, although the image display device disclosed in the Japanese Unexamined Patent Publication No. 7-152009 intends both to prevent the dust from floating in the vicinity of the light incidence/reflection plane of the LCD panel and to prevent the LCD panel and parts thereof from being heated, it employs a cooling system using air in the hermetically closed space and hence it can not be expected to produce a sufficient cooling effect because in recent years a demand for the intensity of the screen image has increased the amount of heat generated by the LCD panel. Therefore, the reliability of the device is not necessarily ensured.
Further, in many devices of color display type among the projection type image display devices epitomized by a LCD projector, a liquid crystal television, and a projection type display device, the images of color components formed by the light valve means like the liquid crystal are often combined together to make a multicolored image. Therefore, the quality of the colored image enlarged and projected on the screen (hereinafter referred to as the screen image") depends to a large degree on convergence performance (convergence adjustment) of converging the positions of the images of color components modulated by the light valves. Therefore, many kinds of techniques relating to a convergence adjustment have been proposed. For example, Japanese Unexamined Patent Publication No. 3-51881 discloses a technique of converging the images by using the convergence adjusting mechanisms provided on the LCD panels of color components. However, in the Japanese Unexamined Patent Publication No. 3-51881, it is not recognized that it is necessary to prevent the dust from floating in the vicinity of the LCD panel and to prevent the LCD panel and parts thereof from being heated.